Cruciate replacing artificial knee

ABSTRACT

A knee joint prosthesis is configured to move between an extended position and a flexion position. The knee joint prosthesis includes a femoral component configured to be mounted to a femur, and a tibial component configured to be mounted to a tibia. The tibial component is configured to engage the femoral component to form the knee joint prosthesis. A post is fixedly connected to one of the femoral component and the tibial component and has a helical surface at a terminal end thereof. A recess is defined on the other of the femoral component and the tibial component and has a helical surface. The helical surfaces of the post and recess are configured to engage in order to cause relative rotation between the femoral and tibial components as the knee joint prosthesis moves between the extended and flexion positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 16/292,467, filed Mar. 5, 2019, which isincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

This invention relates generally to artificial knee prostheses used forTotal Knee Replacement (TKR), and more particularly, to a knee jointprosthesis having an artificial anterior cruciate ligament (ACL) and/orposterior cruciate ligament (PCL).

BACKGROUND OF THE INVENTION

As is described in U.S. Patent App. Pub. No. 2017/0252173 to Garino,which is incorporated by reference herein in its entirety and for allpurposes, prosthetic knees generally include three main components, afemoral component (FIGS. 1A and 1B), which is attached to the distal endof the femur, a tibial component (FIGS. 2A and 2B), which is implantedonto the proximal end of the tibia, and an articular insert (FIGS. 3Aand 3B), which is mounted onto the tibial component and provides africtional surface for the femoral component. The components aredesigned to simulate a joint and the associated mechanics of a humanknee throughout the knee's range of motion. The components are generallyprovided in a variety of shapes with varying dimensions (identified asdimensions A-H and J-T in FIGS. 1A to 3B), so that a physician is ableto select the optimal combination of components depending on thespecific anatomy of the patient. The size and shape of the knee isdependent on various factors including age, gender, and size of thepatient. Therefore, a fairly large inventory of components are generallymade available, so that the prosthetic knee may be tailored for thepatient.

During the course of a routine knee construction with a TKR, the ACL isremoved in a vast majority of all cases and depending on the selectedTKR design, the patient's PCL is either retained or substituted withsome mechanism to replace the lost function of the PCL. Even when thePCL is retained, often a portion of the PCL must be cut or partially cutduring surgery to aid in the balancing of the knee replacement. When thePCL is completely removed, the PCL is substituted by a post and cammechanism.

A TKR generally comprises a femoral component 10, a tibial component 16,and an articular insert 22 that resides on a top mounting portion 20 ofa tibial component 16 for interfacing with the femoral component 10.Referring to FIGS. 1A, 1B, 3A, and 3B, an illustration of a typicaldesign of a post and cam mechanism is provided. An articular insert 22includes an extension 24 that protrudes into an opening 12 of thefemoral component 10. A box 11 having upwardly projecting walls isformed on the interior side of the femoral component 10 and includes aninterior region that intersects the opening 12. The extension 24includes a posterior surface 25 that is intended to be in frictionalcontact with the posterior surface 14 of the opening 12 when the jointis flexed. The resistance generated when the extension 24 bears againstthe posterior surface 14 of the opening 12 in the femoral component 10is intended to simulate the resistance that would have been generated bya healthy posterior cruciate ligament (PCL).

Cam and post mechanisms have been manufactured that partially replacethe function of an ACL by creating a cam surface between the anteriorsurface of the extension 24 and the anterior surface of the opening 12;however, this solution provides only a partial substitution of an ACLbecause the anterior side of the extension 24 is at best able to contactthe anterior side of the opening only between 0 to 20 degrees offlexion.

Another solution is to connect the femoral component and tibialcomponent with a cable-like material, such as the material disclosed inU.S. Pat. No. 5,935,133, the contents of which are incorporated hereinby reference. But this artificial material is typically only used toreplace the PCL and not the ACL.

The lack of an anatomically correct replacement may result in a TKRhaving reduced functionality as compared to the original knee. This maycreate difficulties during physical therapy following surgery, as wellas limit the patient's ability or desire to participate in physicalactivity following therapy. Virtually all modern total knee replacementssacrifice the ACL or inadequately substitute it with a crude cam andpost mechanism, thus leaving the reconstructed knee with kinematicssimilar to that of an ACL-deficient knee. Normal knee kinematicstherefore remain elusive. In addition, the lack of proper interplaybetween an ACL and PCL (which together drive normal knee kinematics)leaves the TKR reconstruction short of producing a relatively normalknee for the patient.

Given the complexity of the mechanics of a knee joint and the difficultyfor patients to adjust to an artificial knee after surgery, ananatomically correct knee replacement system is needed that moreaccurately simulates the resilience and support formerly provided by theremoved ligaments. In order to provide a more anatomically correct TKR,prosthesis embodiments that replicate the function provided by both theACL and PCL are desirable.

Referring now to FIG. 4 , a healthy human knee is illustrated with aloop 30, representing an exemplary artificial ACL/PCL ligament, drawnover the location of the original anatomical ACL and PCL. The section ofthe loop 30 constituting the artificial PCL is bounded by points 26A and26B. The section of the loop 30 constituting the artificial ACL isbounded by points 28A and 28B.

Referring now to FIGS. 5, 6A, and 6B illustrating an embodimentdisclosed in U.S. Patent App. Pub. No. 2017/0252173 to Garino, theconnection points 26 a, 26 b, 28 a, and 28 b of the artificial material,provided as ligament 44, and the lengths spanning between the connectionpoints, provided as an outline of the artificial ligament 44, areconfigured to simulate the dimensions and attachment points of the ACLand PCL in a human knee, as illustrated in FIG. 4 . At least one lengthof artificial ligament may be provided to connect the articular insert22 and femoral component 10 of a TKR.

While U.S. Patent App. Pub. No. 2017/0252173 to Garino providessolutions to these complexities, developments in this area arecontinually sought in the interest of improving the mechanics of a kneejoint.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a knee joint prosthesis iscapable of moving between an extended position and a flexion position.The knee joint prosthesis comprises a femoral component that isconfigured to be mounted to a femur, and a tibial component that isconfigured to be mounted to a tibia, the tibial component beingconfigured to be engaged with the femoral component to form the kneejoint prosthesis. A post is fixedly connected to one of the femoralcomponent and the tibial component and has a helical surface at aterminal end thereof. A recess is defined on the other of the femoralcomponent and the tibial component and has a helical surface. Thehelical surfaces of the post and recess are configured to engage inorder to cause relative rotation between the femoral and tibialcomponents as the knee joint prosthesis moves between the extended andflexion positions.

In another embodiment of the present invention, a knee joint prosthesiscomprises a femoral component that is configured to be mounted to afemur, and a tibial component that is configured to be mounted to atibia, the tibial component being configured to be engaged with thefemoral component to form the knee joint prosthesis. A post is fixedlyconnected to one of the femoral component and the tibial component, anda cam recess is defined on the other of the femoral component and thetibial component and is configured to be engaged by the first post ineither the extended position or the flexion position of the knee jointprosthesis. An artificial ligament is fixedly connected to the femoralcomponent and the tibial component to simulate either an anteriorcruciate ligament or a posterior cruciate ligament. The post and theligament are oriented cross-wise as viewed in a sagittal plane, afrontal plane, or both the sagittal plane and the frontal plane.

In yet another embodiment of the present invention, a knee jointprosthesis comprises a femoral component configured to be mounted to afemur, and a tibial component configured to be mounted to a tibia. Thetibial component is configured to engage the femoral component to formthe knee joint prosthesis. The femoral component and the tibialcomponent are at least partially connected together by a gearedarrangement.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a side view of a femoral component for a knee jointprosthesis known by those of ordinary skill in the art.

FIG. 1B is a bottom view of the femoral component of FIG. 1A.

FIG. 2A is a top view of a tibial component for a knee joint prosthesisknown by those of ordinary skill in the art.

FIG. 2B is a side view of the tibial component of FIG. 2A.

FIG. 3A is a top view of an articular insert for a knee joint prosthesisknown by those of ordinary skill in the art.

FIG. 3B is a front view of the articular insert of FIG. 3B mounted onthe baseplate of a tibial component.

FIG. 4 is a side view of a knee joint illustrating the anatomicallocation of the ACL and PCL and the configuration of an artificialmaterial intended to replace the ACL and PCL.

FIG. 5 is a side view of a femoral component, articular insert, andartificial ligament for a TKR according to the prior art.

FIG. 6A is a top view of a cross-section along line I-I of FIG. 5 .

FIG. 6B is a bottom view of a cross-section along line I-I of FIG. 5 .

FIG. 7A is a cross-sectional side elevation view of a knee jointprosthesis, as viewed in a sagittal plane, according to an exemplaryembodiment of the present invention, wherein the knee joint prosthesisis shown in an extended position.

FIG. 7B is another view of the knee joint prosthesis of FIG. 7A, whereinthe knee joint prosthesis is shown in a flexion position.

FIG. 8 depicts an alternative embodiment of a knee joint prosthesis, asviewed in a sagittal plane, in which the posts are disposed on thefemoral portion and the cams are disposed on the tibial portion.

FIG. 9 depicts an alternative embodiment of the knee joint prosthesis,as viewed in a sagittal plane, in which one post and one cam is disposedon each of the femoral portion and the tibial portion.

FIG. 10A depicts a partial cross-sectional view of an embodiment of aknee joint prosthesis, as viewed in a sagittal plane, in which posts,which mimic the ACL and PCL, are disposed on the tibial portion andengage with cams on the femoral portion.

FIG. 10B depicts the knee joint prosthesis of FIG. 10A, as viewed in afrontal plane.

FIG. 11 depicts an alternative embodiment of a knee joint prosthesis, asviewed in a sagittal plane, in which posts, which mimic the ACL and PCL,are disposed on the femoral portion and engage with cams on the tibialportion.

FIG. 12 depicts an alternative embodiment of a knee joint prosthesis, asviewed in a sagittal plane, in which a post, which mimics the PCL, isdisposed on the tibial portion and engages with a cam on the femoralportion, and an artificial ligament, which mimics the ACL, is disposedbetween the tibial portion and the femoral portion.

FIG. 13 depicts an alternative embodiment of a knee joint prosthesis, asviewed in a sagittal plane, in which a post, which mimics the ACL, isdisposed on the tibial portion and engages with a cam on the femoralportion, and an artificial ligament, which mimics the PCL, is disposedbetween the tibial portion and the femoral portion.

FIG. 14 depicts an alternative embodiment of a knee joint prosthesis, asviewed in a sagittal plane, in which posts, which mimic the ACL and PCL,are disposed on the tibial portion and engage with cams on the femoralportion.

FIGS. 15A and 15B depict side elevation views of an alternativeembodiment of a knee joint prosthesis, as viewed in a sagittal plane, inwhich the tibial portion is coupled to the femoral portion by a gearedarrangement. The knee joint prosthesis is shown in an extended positionin FIG. 15A and a flexion position in FIG. 15B.

FIG. 16A depicts a side elevation view of an alternative embodiment of aknee joint prosthesis, as viewed in a sagittal plane, in which thetibial portion is coupled to the femoral portion by a gearedarrangement, and the geared arrangement is configured to cause medialmovement of the tibial portion upon rotation to the extended position.The knee joint is shown from the posterior side in FIG. 16B, and theanterior side in FIG. 16C.

FIG. 17 depicts an alternative embodiment of a knee joint prosthesis, asviewed in a sagittal plane, in which the tibial portion is coupled tothe femoral portion by a post and cam arrangement.

FIG. 18 depicts an alternative embodiment of a knee joint prosthesis, asviewed in a sagittal plane, in which the tibial portion is coupled tothe femoral portion by a post and cam arrangement.

FIG. 19 is a plan view depicting an alternative embodiment of a kneejoint prosthesis in which the tibial portion is coupled to the femoralportion by a pin and slot arrangement.

DETAILED DESCRIPTION

The present invention provides various embodiments of a knee jointprosthesis. In the figures, ‘A’ represents the anterior side ordirection, ‘P’ represents the posterior side or direction, ‘M’represents the medial side or direction, ‘L’ represents the lateral sideor direction, ‘F’ represents a femoral component, and ‘T’ represents atibial component (or an articular insert that forms part of a tibialcomponent).

FIG. 7A is a cross-sectional side elevation view of a knee jointprosthesis 100, as viewed in a sagittal plane, according to an exemplaryembodiment of the present invention, wherein the knee joint prosthesis100 is shown in an extended position. FIG. 7B is another view of theknee joint prosthesis 100 of FIG. 7A, wherein the knee joint prosthesis100 is shown in a flexion position. The knee joint prosthesis 100 iscapable of rotating between the extended position of FIG. 7A and theflexion position of FIG. 7B.

The prosthesis 100 generally comprises a femoral component 102 and anarticular insert 104 that is either mounted to or forms part of a tibialcomponent.

The femoral component 102 shown in FIGS. 7A and 7B may represent afemoral component (like item 10) having condoyles, or a box (like box11) that is mounted to the femoral component. A recess 108 is formed onthe lower end of femoral component 102. The recess 108 is locatedbetween the condyles 106 along the medial-lateral direction. An edge 111is formed at the semi-circular boundary of the recess 108 at thelocation where the recess 108 intersects the exterior surface of thefemoral component 102. The recess 108 is positioned at the sameapproximate location as the opening 12 in the femoral component 10.Unlike the opening 12, however, the recess 108 is blind, and includes asmooth and rounded interior surface. Two cam surfaces 110 a and 110 b(referred to either individually or collectively as cam surface(s) 110)are formed at opposing ends of the interior surface of the recess 108.Each cam 110 is a smooth and rounded concave surface. The radii of thecams 110 may be the same or different. The cams 110 are configured tointeract with rounded posts 112 a and 112 b extending from the topsurface of the articular insert 104.

The articular insert 104 is similar to the articular insert 22, and theprimary differences between those inserts will be described hereinafter.The articular insert 104 includes the two posts 112 a and 112 b(referred to either individually or collectively as post surface(s) 112)that extend from the bearing surface 113. Post 112 a corresponds to theACL, whereas the post 112 b corresponds to the PCL. Each rounded post112 terminates at a convexly rounded surface. The radius of each post112 may be identical to or substantially the same as the radius of eachcam 110. The extension height and radii of the posts 112 may bedifferent (as shown) or the same to complement the geometry of themating cams 110. According to this embodiment, the ACL post 112 a has agreater height than the PCL post 112 b. The posts 112 extend along theirrespective axes Z, which are orthogonal to bearing surface 113.Alternatively, the posts 112 may extend obliquely with respect to axisZ. The posts 112 of FIG. 7A, as well as all of the other posts describedherein, may be integral with the articular insert 22 (or other componentto which the post is connected), as shown, or connected to the articularinsert 22 using mechanical threads, a bolt, friction, adhesive, cement,or any other means for mounting two components together that are knownto those skilled in the art.

The articular insert 104 is capable of rotating relative to the femoralcomponent 102 between the extended position of FIG. 7A and the flexionposition of FIG. 7B. In the extended position of the knee jointprosthesis 100, the condyles may rest on the bearing surface 113 of thearticular insert 104, and the posts 112 are positioned against theirrespective cams 110. As the femoral component 102 rotates relative tothe articular insert 104, or vice versa, the post 112 rides along thesurface of cam 110 until the edge 111 of the recess 108 bears on thebase of the posterior post 112. The ACL post 112 a may bear on its cam110 a. Although not shown, the collateral ligaments (MCL and LCL)adjacent to the knee joint prosthesis 100 prevent detachment of thefemoral component 102 from the articular insert 104.

The arrangement of two posts 112 and two cams 110 more closely mimicsthe arrangement of the PCL and ACL, as compared to a traditional kneejoint prosthesis having a single post and a single cam.

As noted above, the recess 108 may be formed in a separate insert, likebox 11, that is capable of being attached to the femoral component 102.A series of inserts having different recess geometries may be providedas a kit, such that a medical professional can select the insert havinga geometry that is best suited for the particular anatomy of a patient.

FIG. 8 depicts a knee joint prosthesis 118 in which the posts 122 a and122 b are disposed on the femoral component 124 and the cams 128 aredefined on a recess 130 that is disposed on the articular insert 132 ofa tibial component. The knee joint prosthesis 118 is similar to the kneejoint prosthesis 100 with the exception that the location of the postsand cams are switched. Operation of the knee joint prosthesis 118 issubstantially similar to that of the knee joint prosthesis 100. Althoughnot shown, like box 11, the posts 122 a and 122 b may be formed in aseparate insert that is capable of being attached to the femoralcomponent 124.

FIG. 9 depicts a knee joint prosthesis 136. The knee joint prosthesis136 is similar to the knee joint prosthesis 100 with the exception thatone post 138 and one cam recess 140 are disposed on the femoralcomponent 142, and one post 144 and one cam recess 146 are disposed onthe articular insert 148 of a tibial component. In the extended positionshown in FIG. 9 , the post 138 of the femoral component 142 is mountedwith the cam recess 146 of the tibial articular insert 148, and the post144 of the tibial articular insert 148 is mounted with the cam recess140 of the femoral component 142. Although the post 138 is disposedanterior of recess 140, it should be understood that the locations ofthe post 138 and the recess 140 may be switched (along with thelocations of the recess 146 and the post 144). Operation of the kneejoint prosthesis 136 is substantially similar to that of the knee jointprosthesis 100.

FIGS. 10A and 10B depicts an embodiment of a partial cross-sectionalview of a knee joint prosthesis 150. The prosthesis 150 is similar tothe prosthesis 100 and only the primary differences therebetween will bedescribed. In the knee joint prosthesis 150, the posts 152 a and 152 b(referred to collectively as posts 152), which more closely mimic thePCL and ACL, respectively, are disposed on the articular insert 154 of atibial portion (or the tibial portion itself) and engage with cams 156 aand 156 b (referred to collectively as cams 156), respectively, disposedon a recess 157 that is formed on the femoral component 158. The recess157 extends upwardly from the bearing surface 155 of the prosthesis 150.

Specifically, the post 152 a, which extends from the lateral andposterior sides of the articular insert 154 to the medial and anteriorsides of the femoral component 158, more closely mimics the location andgeometry of the PCL. The post 152 b, which extends from the medial andanterior sides of the articular insert 154 to the lateral and posteriorsides of the femoral component 158, more closely mimics the location andgeometry of the ACL. The posts 152 a and 152 b are oriented cross-wiseas viewed in the sagittal and frontal planes, however, the posts 152 aand 152 b may be oriented cross-wise as viewed in only one of thoseplanes.

The angle ‘B’ of each post 152 with respect to the bearing surface 155,as viewed in a sagittal plane, may vary from that which is shown, andmay be tailored to approximate the exact angle of an ACL or PCL.Similarly, the angle ‘D’ of each post 152 with respect to the bearingsurface 155 of the articular insert 154, as viewed in a frontal plane,may vary from that which is shown, and may be tailored to approximatethe exact angle of an ACL or PCL. It is noted that the angles B and Dmay be exaggerated in the figures. The length and diameter of each post152 may vary from that which is shown, and may be tailored toapproximate that of an ACL or PCL. Each post 152 may not necessarilyextend straight along a longitudinal axis, as shown, and may instead becurved to approximate the curved shape of an ACL or PCL.

Each post 152 includes a convex rounded surface that rotatably andslidably engages with a concave surface of a cam 156 of the recess 157.It is noted that the posts 152 and cams 156 are in sliding contact, butare physically detached from each other. Although not shown, the recess157 may be formed in a separate insert, like box 11, that is removablyattached to the femoral component 158.

FIG. 11 depicts an alternative embodiment of a knee joint prosthesis160, which is similar to the knee joint prosthesis 150 with theexception that the posts 159 a and 159 b are disposed on the femoralcomponent 162 and engage with cams 161 a and 161 b, respectively,disposed on a recess 163 that is formed on the articular insert 165 of atibial portion (or the tibial portion itself). The locations of theposts and cams are interchangeable, however, it is noted that thelocation and geometry of the posts 159 a and 159 b continue to mimicthat of an ACL and PCL, respectively. Also, like the embodiment shown inFIG. 9 , and although not shown, each of the articular insert 165 andthe femoral component 162 may include one angled post and one cam.

FIG. 12 depicts an alternative embodiment of a knee joint prosthesis180. The knee joint prosthesis 180 is similar to the knee jointprosthesis 150, and the primary differences will be describedhereinafter. In the knee joint prosthesis 180, a post 182, which mimicsthe PCL, is disposed on the tibial portion 184 and engages with a camrecess 186 on the femoral portion 188. An artificial ligament 190, whichmimics the ACL, is fixed to the tibial portion 184 and the femoralportion 188. Fixation is denoted by the small ‘xxx’ characters in FIG.12 .

The post 182 extends from the lateral and posterior sides of thearticular insert 184 to the medial and anterior sides of the femoralcomponent 188 to mimic the location of the PCL. The ligament 190 extendsfrom the medial and anterior sides of the articular insert 184 to thelateral and posterior sides of the femoral component 188 to mimic thelocation of the ACL. The ligament 190 is fixedly connected to both thearticular insert 184 and the femoral component 188, unlike the post 182.The post 182 and the ligament 190 are oriented cross-wise as viewed inthe sagittal and frontal planes, however, the post 182 and the ligament190 may be oriented cross-wise as viewed in only one of those planes.

FIG. 13 depicts an alternative embodiment of a knee joint prosthesis 192that is similar to the prosthesis 180 with the exception that thelocations of the ligament 190′ and the post 182′ are switched, such thatthe ligament 190′ represents the PCL and the post 182′ represents theACL. As an alternative to FIGS. 12 and 13 , the post 182 may be omittedentirely if the natural ACL or PCL of the patient is preserved in apartial knee replacement.

The ligaments shown herein are formed from an artificial material,preferably a synthetic fiber or cord, to replace an ACL or PCL, suchthat the artificial material is configured similarly to the respectiveorientation and location of the ACL and PCL in a normal knee.Specifically, the configuration is such that the origin and insertionpoints of the artificial material in a TKR is similar to the origin andinsertion points of the ACL and PCL in a normal knee.

FIG. 14 depicts an alternative embodiment of a knee joint prosthesis200, which is similar to the knee joint prosthesis 150 with theexception that the free end of the PCL post 202 includes a helicalprotrusion 204, which may be mechanical threads. The cam 206 in thefemoral component, which receives the helical protrusion 204, includes ahelical recess 208. The helical recess 208 interacts with the helicalprotrusion 204 to cause slight rotation about axis Y as the knee jointprosthesis 200 moves between the extended and flexion positions. Theslight rotation mimics the slight rotation experienced in a real kneejoint when becoming fully extended. The helical surfaces 204 and 208may, alternatively, be provided in the form of wedged, angled or slopingsurfaces.

It should be understood that the term “artificial” means only that it isnot the original anatomical ACL or PCL ligament in its original formprior to the TKR, and should not be interpreted as a limitation to theuse of only synthetic materials. Accordingly, the artificial ligament,may comprise “natural” materials, such as materials fashioned frombiologically created materials and/or may comprise a hybrid of syntheticand natural materials. Other exemplary materials may comprise a variantof a woven polyethylene similar to material previously marketed asSecureStrand® cable, a braided, ultra high molecular weight polyethylene(UHMWPE) cable used for surgical fixation in posterior spinalreconstruction, material currently marketed as Super Cables® (Kinamed,Inc., Camarillo, Calif.) made from UHMWPE and Nylon 6/6,6, Gore-tex®(PTFE fiber manufactured by W.L. Gore and Associates, Inc. Newark,Del.), carbon fiber, or other similar woven materials.

According to various embodiments of the present invention, theartificial material in the form, for example, of artificial ligament maybe incorporated into the TKR either at the time of surgery or the TKRmay be pre-assembled with the artificial material in advance of surgery.Various methods and devices for connecting the ligament to the tibialand femoral components are described in U.S. Patent App. Pub. No.2017/0252173 to Garino. As is described in that reference, the lockingmechanism for the ends of the artificial ligaments are not limited toany particular construction, and may comprise a spherical retainer, ametal clip, a hook, loops, a fastener in the form of a nail, forexample.

In review of the above-described embodiments it should be appreciatedthat the posts, cams and ligaments can be positioned on or connected todifferent components and in different locations. Thus, theabove-described embodiments should not be viewed as limiting.

FIGS. 15A and 15B depict side elevation views of an alternativeembodiment of a knee joint prosthesis 300, as viewed in a sagittalplane, in which the tibial portion 302 is coupled to the femoral portion304 by a rack and pinion type geared arrangement. It should beunderstood that the portion of the knee joint prosthesis 300 shown inFIGS. 15A and 15B does not represent the entire knee joint prosthesis.Rather, the portion of the knee joint prosthesis 300 shown in FIGS. 15Aand 15B represents the portions of the tibial portion 302 and femoralportion 304 that contact each other within the area of the box (like box11). The knee joint prosthesis 300 is shown in an extended position inFIG. 15A and a flexion position in FIG. 15B. The teeth 306 on the tibialportion 302 are meshed with the teeth 308 of the femoral portion 304,such that rotation of the tibial portion 302 causes rotation of thefemoral portion 304, and vice versa.

FIGS. 16A-16C depicts an alternative embodiment of a knee jointprosthesis 400, in which the tibial portion 402 is coupled to thefemoral portion 404 by a geared arrangement. The knee joint prosthesis400 is substantially similar to the knee joint prosthesis 300 and theprimary differences between those embodiments will be describedhereinafter.

The tibial portion 402 includes a rounded and convex outer surface uponwhich teeth 406 are disposed. The convex outer surface includes aposterior segment 406 a having a simple curved path that follows the arcof a circle, and an anterior segment 406 b that follows a helical path.The helical path extends medially as viewed in an anterior direction.The teeth also follow the trajectory of the helical path of the anteriorportion 406 b. The posterior segment 406 a intersects the anteriorsegment 406 b in a graduated manner.

Similarly, the femoral portion 404 includes a convex outer surface uponwhich teeth 408 are disposed. The convex outer surface includes aposterior segment 408 a having a simple curved path that follows the arcof a circle, and an anterior segment 408 b that follows a helical path.The helical path extends medially as viewed in an anterior direction. Itshould be understood that the teeth also follow the trajectory of thehelical path of the anterior segment 408 b. The posterior segment 408 aintersects the anterior segment 408 b in a graduated manner.

Although both the posterior segment 408 a and the anterior segment 408 bare shown and described as following a helical trajectory, only one ofthose segments may follow a helical trajectory.

The teeth 406 on the tibial portion 402 are meshed with the teeth 408 ofthe femoral portion 404, such that rotation of the tibial portion 402causes rotation of the femoral portion 404, and vice versa. Also, as thetibial portion 402 rotates in an anterior direction to the extendedposition, the tibial portion 402 also moves in the medial direction. Theslight rotation of the tibial portion 402 in the medial direction mimicsthe slight rotation experienced in a real knee joint when becoming fullyextended. Rotation in the medial direction is due to the helicalgeometry of the mating anterior portions 406 b and 408 b.

FIG. 17 depicts an alternative embodiment of a knee joint prosthesis500, as viewed in a sagittal plane, in which the tibial portion iscoupled to the femoral portion by a post 502 and cam 504 arrangement.The knee joint prosthesis 500 is substantially similar to the knee jointprosthesis 300 with the exception that the teeth 306 and 308 arereplaced by posts 502 and cams 504, respectively. It should beunderstood that the teeth 406 and 408 of the knee joint prosthesis 300may similarly be replaced by a post and cam arrangement like that of theknee joint prosthesis 500.

As shown in FIG. 18 , the placement of the posts 506 and cams 508 can beswitched without departing from the scope or spirit of the invention.

FIG. 19 is a plan view depicting an alternative embodiment of a kneejoint prosthesis 600 in which the tibial portion T is coupled to thefemoral portion F by a pin 602 and slot 604 arrangement. The knee jointprosthesis 600 is shown in the flexion position in FIG. 19 . Like theother embodiments, the portion of the knee joint prosthesis 600 shown inFIG. 19 merely represents the portions of the tibial portion T and thefemoral portion F that contact each other within the area of the box(like box 11), as opposed to an entire knee joint prosthesis.

According to this embodiment, the pin 602 is disposed on the femoralportion F and the slot 604 is disposed on the tibial component T,however, the opposite could be true. The pin 602 extends in a verticaldirection into the depth of the slot 604. In operation, the pin 602travels along the length of the slot 604. The slot 604 curves in themedial direction as viewed in an anterior direction.

In operation, as the tibial portion T rotates in an anterior directionto the extended position and the pin 602 travels along the length of theslot 604, the tibial portion T also rotates in the medial direction. Theslight rotation of the tibial portion T in the medial direction mimicsthe slight rotation experienced in a real knee joint when becoming fullyextended. Movement in the medial direction is due to the curvature ofthe slot 604.

The components of the knee joint prosthesis may be made of the same orsimilar material. In general, however, all materials are preferablyinert, not prone to cause infection, and otherwise safe and approved foruse as a surgical implant. Exemplary materials include polyethylene,surgically approved metal alloys, surgically approved ceramic materials,or a combination thereof. Any well-known materials in the field ofsurgical implants may be used to fabricate any of the variousembodiments or portions thereof according to the present invention.

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes, andsubstitutions may occur to those skilled in the art without departingfrom the spirit of the invention. Accordingly, it is intended that theappended claims cover all such variations that fall within the spiritand scope of the invention.

I claim:
 1. A knee joint prosthesis configured to move between anextended position and a flexion position, the knee joint prosthesiscomprising: a femoral component configured to be mounted to a femur; atibial component configured to be mounted to a tibia, the tibialcomponent configured to engage the femoral component to form the kneejoint prosthesis; a first post fixedly connected to one of the femoralcomponent and the tibial component and having a helical surface at afree end thereof, a first recess defined on the other of the femoralcomponent and the tibial component and having a mating helical surface,wherein the helical surfaces of the first post and first recess areconfigured to engage in order to cause relative rotation between thefemoral and tibial components as the knee joint prosthesis moves betweenthe extended and flexion positions a second post fixedly connected toone of the femoral component and the tibial component, and a second camrecess defined on the other of the femoral component and the tibialcomponent that is configured to be engaged by the second post.
 2. Theknee joint prosthesis of claim 1, wherein the first post is fixedlyconnected to the femoral component, and the first recess is defined inthe tibial component.
 3. The knee joint prosthesis of claim 1, whereinthe first post is fixedly connected to the tibial component, and thefirst recess is defined in the femoral component.
 4. The knee jointprosthesis of claim 1, wherein the first post and the second post areoriented cross-wise in both a sagittal plane and a frontal plane.
 5. Theknee joint prosthesis of claim 1, wherein the second post includes arounded convex surface at a free end thereof and the second cam recessis a rounded concave surface.
 6. The knee joint prosthesis of claim 1,wherein the second post is slidingly engaged with yet disconnected fromthe second cam recess.
 7. The knee joint prosthesis of claim 1, whereinthe tibial component comprises an articular insert.
 8. The knee jointprosthesis of claim 1, wherein the first post forms part of a removableinsert that is configured to be connected to either the femoralcomponent or the tibial component.
 9. The knee joint prosthesis of claim1, wherein the helical surface of the first post extends into the matinghelical surface of the first recess.
 10. The knee joint prosthesis ofclaim 1, wherein the first post is connected to the tibial component andextends in an anterior direction from a mating surface of the tibialcomponent.